The communications industry is using more and more optical or light fibers in lieu of copper wire. Optical fibers have an extremely high bandwidth thereby allowing the transmission of significantly more information than can be carried by a copper wire transmission line such as twisted pairs or coaxial cable.
Modern telephone systems require bi-directional communications where each station or user on a communication channel can both transmit and receive. This is true, of course, whether using electrical wiring or optical fibers as the transmission medium. Early telephone communication systems solved this need by simply providing separate copper wires for carrying the communications in each direction, and this approach is still used in older installations where telephony is the only required service. It is also often used even where digital transmission service is demanded as the signals get closer to the end users. Although twisted pairs and coaxial cables are used in homes and distribution terminals close to the home end user, some modern telecommunication systems now use microwave and optic fibers as transmission mediums.
Because of extremely high bandwidths available for use by an optical fiber, a single fiber is quite capable of carrying a great number of communications in both directions. One technique of optical transmission is WDM (wavelength divisional multiplexing) and uses different wavelengths for each direction of travel.
However, because of the extremely high bandwidths of optical fibers, the use of an optical fiber solely as a telephone path is still a very ineffective use of the fiber and, in fact, the available bandwidth of an optical fiber makes it possible to use a transmission technique at one wavelength for telephony and then by the use of WDM technology to use another technique at a second wavelength.
Another area of rapidly growing technology is providing unidirectional TV signals by cable to a multiplicity of subscribers or users (broadcast and/or multicast). In the past, such signals were and still are typically transmitted as electrical signals on coaxial cables (e.g., cable TV). However, the use of optical fibers for transmission allows broadband transmission to a large number of customers and, since the bulk of the transmission of TV signals is one way (i.e., unidirectional), if a single optical fiber were used solely for the TV signals, there would be wasted wavelengths of light.
Therefore, techniques for transmitting bidirectional telephony signals, bidirectional DSL signals and primarily unidirectional TV signals make more efficient use of an optical fiber. However, along with all new technology there usually appears another set of major problems that were either not present in the old technology or were only minor problems. One problem with optical communication systems that provide both digital CATV signals at about 1530/1560 nanometers wavelength of light and digital voice/data signals at around 1310/1490 nanometers wavelength of light is power equalization outputs at the multiple ports.